FMRI Brain Activation of Aripiprazole Treatment in Autism Spectrum Disorders

Inclusion Criteria: * male or female of any race or ethnicity * ambulatory status (outpatient) at time of consent * age 10-55 inclusive at time of consent * clinical diagnosis of autism spectrum disorder and meets screening criteria on the Social Communication Questionnaire as well as either the Autism Diagnostic Observation Schedule (ADOS) or the Autism Diagnostic Interview-Revised (ADI-R) administered by raters trained to research reliability. * estimated IQ greater than 70 and capable of making an informed decision based on assessment of their understanding and judgment * Children's Yale-Brown Obsessive Compulsive Scale: Modified for Pervasive Developmental Disorders (PDD-CYBOCS) \> 8 as assessed during telephone screening. * Free of psychoactive medication for at least: one month for fluoxetine; two weeks for other SSRIs and neuroleptics; and five days for stimulants prior to MRI scanning \[excepting stable doses (greater than three months duration) of anticonvulsant medication for seizure disorder\] * Currently taking psychoactive medication that is not providing sufficient relief of repetitive behaviors and willing to discontinue all psychoactive medication for the duration of the study. * Judged reliable for medication compliance and agreeing to keep follow-up study appointments. Exclusion Criteria: * Age less than 10 years or greater than 55 years at time of consent * Estimated IQ less than 70 * Uncontrolled epilepsy (seizure within 6 months prior to consent) * Presence of medical conditions that might interfere with participation, or where participation would be contraindicated. * History of neurological injury: head trauma, poorly-controlled seizure disorder (seizure within the preceding six months), stroke, prior neurosurgery, or under the care of a neurologist or neurosurgeon as determined by interview * History of claustrophobia * Implanted or irremovable metal in the body (including certain tattoos and permanent make-up). * Current pregnancy in females * Inability to communicate satisfactorily and directly (without a translator) in English * Medical contraindications to aripiprazole therapy as determined by history (including induction of neuroleptic malignant syndrome, dystonic reaction, or known drug allergy) * Ongoing need for psychoactive medication other than study medication \[excepting stable doses (greater than 3 months duration) of anticonvulsant medication for seizure disorder or diphenhydramine for sleep * prior history of aripiprazole treatment failure at appropriate doses and duration * clinically significant low white blood cell count at baseline